The present invention relates to methods and apparatus for automatic test inspection. Merely by way of example, the invention is illustrated as an automatic inspection method and apparatus for classification of defects, more specifically for detection of "Mura"-type defects in substrates. Substrates include liquid crystal flat panel displays, active matrix displays and the like.
The uses of a liquid crystal flat panel displays (LCFPD) or the like continue to grow rapidly. Consumer items such as portable video recorders, pocket televisions, notebook computers, engineering work-stations, high-definition televisions (HDTV), and the like incorporate such displays. Based upon the continued demand for such displays, the industry have made massive capital investments to create state-of-art manufacturing lines.
Despite such capital outlay, however, the industry still rely primarily upon human test operators to perform the final test and inspection of such substrates. The test operator performs a variety of visual inspections of each display for defects and accepts or rejects the display based upon the operator's perceptions. The quality and completeness of the inspection is dependent on the individual test operator, who has been trained using limited samples of displays that are characterized as passing or failing. Accordingly, the inspection results are highly subjective, prone to error, and cannot be used consistently and efficiently to monitor, control, and improve the quality of the various manufacturing processes. In addition, the subjective testing criteria results in a lack of industry wide quality standards.
Effective process monitoring and control of LCFPD production cycle is possible only through quantitative and qualitative inspection methods by way of automatic inspection machines. An example of one of the first automatic inspection apparatus was conceived by Photon Dynamics, Inc. (PDI) in 1992, assignee of the present application. FIG. 1 shows the role of an automatic inspection apparatus during the final testing stages of the LCFPD manufacturing processes 10. The LCFPD undergoes completion, step 12, first inspection via flat panel inspection apparatus, step 14, module assembly, step 16, second inspection via flat panel inspection apparatus, step 18, shipment, step 20, and incoming inspection via flat panel inspection apparatus, step 22. A communication network 24 provides an interface between each of the inspections at the flat panel inspection system and a process control work-station 26.
Major classes of LCFPD defects encountered at the final inspection are often pixel defects or wide-area pixel defects (also known as Mura defects). Problems in the manufacturing process of the LCFPD often cause Mura defects. Because certain manufacturing problems cause certain types of Mura defects, thus identification and elimination of the manufacturing problems often leads to the reduction of Mura defects during subsequent processing runs. However, it is often difficult to recognize the Mura defects by category and relate such defect to a step in the manufacture process. In particular, the Mura defects are often too difficult for the test operator to identify easily, and to categorize efficiently and cost effectively. Accordingly, no easy way of identifying defect types and categorizing such defects for analysis presently exists.
From the above, it is seen that methods and apparatus for the efficient identification, and classification of defects such as Mura defects and the like are often desirable.